Sleeper block units are used in so-called slab tracks which are increasingly preferred to so-called ballasted tracks since they allow an increased performance of the track with regard to the attainable speeds and reduced maintenance costs. Such sleeper block units generally comprise a block made of concrete, a shoe generally made of shaped rubber that receives the block, and a resilient elastomer pad that is arranged between the bottom of the block and the bottom of the shoe. On the upper side of the block, a fastening system for a rail is arranged. The shoe is encased in concrete.
In patent DE10196374B4 it is explained that in such sleeper block units the dynamic to static rigidity ratio increases with the vertical movement of the block and therefore the deformation of the elastomer pad under dynamic loads is impeded by an interface between the block and the shoe wall, and that this interface is a phenomenon known as the wedge effect. The cited patent then describes a solution for eliminating the wedge effect without reducing the lateral resistance of the track and for decreasing the dynamic to static rigidity ratio. It is evident that the rigidity and the damping behavior of a sleeper block unit are adversely influenced when water, dust, dirt, laitance or the like enter between the block and the shoe, particularly when infiltrated water freezes. Therefore, measures aiming to seal the space between the block and the shoe have already been suggested.
The references EP1017906B1 and DE4335516A1 both show a sleeper block having a partly surrounding sleeper shoe where a resilient sealing lip lying against the substantially vertically oriented outer wall of the sleeper block is arranged at the upper edge of the sleeper shoe. These arrangements suffer from the disadvantage that during vertical movements of the sleeper block the sealing lip rubs against the outer wall of the sleeper block and is therefore subject to wear so that the sealing effect decreases over time. The reference EP0915202A1 describes a sleeper block and sleeper shoe assembly where the latter has a surrounding sealing arrangement at its upper edge that sealingly engages in a dedicated surrounding groove in the sleeper block. This groove complicates the manufacture of the sleeper block. Ultimately, patent application FR2840330A1 describes a sleeper block and sleeper shoe assembly where the latter has a relatively complicated sealing arrangement at its upper edge that is produced by means of a flowable sealing material.
On the background of this prior art it is the object of the invention to provide a sleeper block unit of the kind mentioned in the introduction where the sealing arrangement is of simple design and nevertheless subject to little wear in operation.